Treatment of peptic ulceration by suppression of gastric aeid, secretion with the histamine H,-receptor antagonist, cimetidine is now well established. Prior to the availability of ranitidine, cimetidine was the only histamine H2-receptor antagonist available for treatment of duodenal and gastric ulceration. The aim of this study was to compare the efficacy of ranitidine and cimetidine in accelerating the healing of duodenal ulcer. The therapeutic trials comparing ranitidine with cimetidine in a total of 44. out-patients with endoscopically diagnosed duodenal ulcer ivere entered into the study. 28 patients were treated with ranitidine 150mg twiee daily, and 16 patients with cimetidine 200 mg 4 times daily for 4 weeks. Overall endoscopic healing rates were 75%, on ranitidine and 64.3% on cimetidine, and so ranitidine appears to be slightly more effective than cimetidine although too small numbers af patients were studied to detcet any difference between drugs. Aa ranitidine is effective with administration twice daily, patient compliance may be better than with the 4 times daily treatment regimen adopted with cimetidine, though has not yet to be adequately demonstrated. There were no significant side-effects, either ranitidine or cimetidine, to the administration of the drug, except a case of dyspepsia on cimetidine regimen.